An orthosis is any apparatus that may be used to correct or support parts of the body to improve function, reduce discomfort, or to provide increased mobility for a patient. Orthoses are available to address medical problems with parts of the lower body, including the hip, leg, knee, ankle, and foot.
A nonexhaustive list of orthoses includes, an ankle-foot orthosis (AFO), a knee-ankle-foot orthosis (KAFO), a hip-knee-ankle-foot orthosis (HKAFO), and a foot orthosis (FO).
A common feature among all the orthoses types is the ability to adjust, modify, or make a correction to ideally suit the orthosis to the patient for which it is intended. For example, many orthoses, especially orthoses for joints, can be made more or less stiff. Additionally, the shank angle may also be adjusted.
Referring to FIG. 1A, an AFO 100 is illustrated. An AFO helps to support the foot in relation to the ankle joint. One particular AFO is a molded piece of semirigid material, such as plastic or carbon fiber, having a sole portion 102 connected to a heel cup 104 and an Achilles portion 106 extending upwards along the Achilles tendon that terminates at or near the calf muscles. The Achilles portion 106, which extends upwards, can wrap around the lower leg, and may even extend anteriorly. The Achilles portion 106 may be secured to the lower leg, while the sole portion is secured to the foot. The amount of material that is used in the upwardly extending Achilles portion determines the stiffness and/or the shank angle of the AFO 100 with respect to ankle joint stiffness and foot dorsiflexion. The stiffness may be considered, in part, to be the degree to which the Achilles portion is resistance to flexing with respect to the foot sole. The shank angle may be considered the angle between the upright portion (Achilles portion) and the foot sole. An AFO may be prescribed to a patient with weakened plantar flexor muscles. When these muscles are working properly, they store energy much like a spring. This energy is released during walking in the propulsion or push-off phase. Thus, a person with functioning muscles can be more energy efficient during walking. However, a patient with weakened muscles has a reduced ability to store or release energy in the ankle. Thus, an AFO is prescribed to replace the function of the weakened muscles. An AFO must behave like a spring; thus, it must be flexible and have memory so that it returns to its original configuration. Like a spring, an AFO has a certain degree of stiffness and a certain shank angle. Many AFOs can be tuned to change the stiffness and/or shank angle.
As shown in FIG. 1B, an AFO 108 may begin as a “universal” AFO 108, which includes extensive wrap around sides. Depending on the condition of the patient, the universal AFO 108 can be modified by cutting along the dotted trimming lines 110 shown in FIG. 1B. By cutting greater amounts of material, the orthosis stiffness is reduced.
FIG. 1C shows an alternative AFO 112 including a foot sole 116 with heel cup and an Achilles portion 114, which attaches to the distal part of the leg. Unlike the AFO illustrated in FIGS. 1A and 1B, the AFO illustrated in FIG. 1C comprises two molded pieces of plastic which are attached to each other at a pivoting hinge 118. Thus, stiffness and shank angle is adjusted in the articulated AFO by manipulating a property of the joint 118 between the sole 116 and the Achilles portion 114.
In order to prescribe an orthosis with the proper stiffness and/or shank angle, an orthotist may rely on experience, clinical examination, or a patient interview. However, the orthotist does not have many other tools at his disposal for prescribing the suitable stiffness and/or shank angle of an orthosis.